Power transmission apparatus for vehicle

ABSTRACT

A power transmission apparatus may include a first input shaft fixedly connected to an engine output shaft, a second input shaft mounted external to the first input shaft, a third input shaft mounted and external to the second input shaft, an intermediate shaft and first and second output shafts, an idle shaft mounted in parallel with the second output shaft, a planetary gear mounted on an axis of the intermediate shaft, a plurality of gear sets the first, and second output shafts, the idle shaft, and the planetary gear set, a first synchronizer mounted on the first output shaft, a second synchronizer mounted on the second output shaft, selectively receiving a torque from the third input shaft through two paths, and transmitting the received torque to the second output shaft, and four clutches each of which facilitating selective connection.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority to Korean Patent Application No.10-2019-0065336 filed on Jun. 3, 2019, the entire contents of which isincorporated herein for all purposes by this reference.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a power transmission apparatus for avehicle. More specifically, the present invention relates to a powertransmission apparatus for a vehicle which may realize a plurality ofshifting stages in a minimal configuration, wherein the shift-stage isarbitrarily selected according to characteristics of the vehicle toimprove power delivery performance and fuel consumption, down-size toimprove the installability of the power transmission apparatus for avehicle.

Description of Related Art

Research on realizing more shifting stages of an automatic transmissionare undertaken to achieve enhancement of fuel consumption and betterdrivability, and recently, increase of oil price is triggering a hardcompetition in enhancing fuel consumption of a vehicle.

In the present sense, research on an engine has been undertaken toachieve weight reduction and to enhance fuel consumption by so-calleddownsizing research on an automatic transmission has been performed tosimultaneously provide better drivability and fuel consumption byachieving more shifting stages.

To achieve more shifting stages for an automatic transmission, thenumber of parts is typically increased, which may deteriorateinstallability, production cost, weight and/or power flow efficiency.

Therefore, to maximally enhance fuel consumption of an automatictransmission having more shifting stages, it is important for betterefficiency to be derived by fewer number of parts.

In the present respect, an eight-speed automatic transmission has beenrecently introduced, and a planetary gear train for an automatictransmission facilitating more shifting stages is under investigation.

An automatic transmission of eight or more shifting stages typicallyincludes three to four planetary gear sets and five to seven engagementelements (friction elements), and may easily become lengthy,deteriorating installability.

In this regard, disposing planetary gear sets in parallel or employingdog clutches instead of wet-type control elements is attempted. However,such an arrangement may not be widely applicable, and using dog clutchesmay easily deteriorate shift-feel.

The information included in this Background of the Invention section isonly for enhancement of understanding of the general background of theinvention and may not be taken as an acknowledgement or any form ofsuggestion that this information forms the prior art already known to aperson skilled in the art.

BRIEF SUMMARY

Various aspects of the present invention are directed to providing apower transmission apparatus configured for a vehicle having advantagesof improvement of power delivery performance and fuel consumption

A power transmission apparatus configured for a vehicle according tovarious exemplary embodiments of the present invention may include afirst input shaft fixedly connected to an engine output shaft, a secondinput shaft formed as a hollow shaft, mounted coaxial with and externalto the first input shaft without rotational interference therebetween,and selectively connectable to the first input shaft, a third inputshaft formed as a hollow shaft, mounted coaxial with and external to thesecond input shaft, and selectively connectable to the first inputshaft, an intermediate shaft and first and second output shafts mountedin parallel with the first, second, and third input shafts, an idleshaft mounted in parallel with the second output shaft, a planetary gearset having first, second, and third rotation elements and mounted on anaxis of the intermediate shaft, the third rotation element and one ofthe first and second rotation elements being selectively connectable tothe intermediate shaft, the first and second rotation elements beingcoupled to the third and second input shafts, a plurality of gear sets,each of which is configured to allow at least one torque flow betweenthe intermediate shaft, the first, second, and third input shafts, thefirst, and second output shafts, the idle shaft, and the planetary gearset, a first synchronizer mounted on the first output shaft, selectivelyreceiving a torque from the second input shaft through two paths, andtransmitting the received torque to the first output shaft, a secondsynchronizer mounted on the second output shaft, selectively receiving atorque from the third input shaft through two paths, and transmittingthe received torque to the second output shaft, and four clutches eachof which facilitating selective connection.

The planetary gear set may be a single pinion planetary gear set and thefirst, second, and third rotation elements may be a sun gear, a planetcarrier, and a ring gear.

The first and third rotation elements of the planetary gear set may beselectively connectable to the intermediate shaft. The four clutches mayinclude a first clutch mounted between the first input shaft and thesecond input shaft, a second clutch mounted between the first inputshaft and the third input shaft, a third clutch mounted between theintermediate shaft and the third rotation element of the planetary gearset, and a fourth clutch mounted between the intermediate shaft and thefirst rotation element of the planetary gear set.

The second and third rotation elements of the planetary gear set may beselectively connectable to the intermediate shaft.

The four clutches may include a first clutch mounted between the firstinput shaft and the second input shaft, a second clutch mounted betweenthe first input shaft and the third input shaft, a third clutch mountedbetween the intermediate shaft and the third rotation element of theplanetary gear set, and a fourth clutch mounted between the intermediateshaft and the second rotation element of the planetary gear set.

The plurality of gear sets may include a first gear set including afirst input gear and a first external gear, the first input gear beingfixedly connected to the first input shaft, the first external gearbeing fixedly connected to the intermediate shaft and externallygear-meshed with the first input gear, a second gear set including asecond input gear and a first shifting gear, the second input gear beingfixedly connected to the second input shaft, the first shifting gearbeing rotatably mounted on the first output shaft and externallygear-meshed with the second input gear, a third gear set including asecond external gear, a third input gear, and a second shifting gear,the second external gear being fixedly connected to the second rotationelement of the planetary gear set, the third input gear being fixedlyconnected to the second input shaft and externally gear-meshed with thesecond external gear, and the second shifting gear being rotatablymounted on the first output shaft and externally gear-meshed with thethird input gear, a fourth gear set including a third external gear anda fourth input gear, the third external gear being fixedly connected tothe first rotation element of the planetary gear set, the fourth inputgear fixedly connected to the third input shaft and externallygear-meshed with the third external gear, a fifth gear set including athird shifting gear and an second idle gear, the third shifting gearbeing rotatably mounted on the second output shaft, the second idle gearbeing fixedly connected to the idle shaft and externally gear-meshedwith the third shifting gear, a sixth gear set including the fourthinput gear and a fourth shifting gear, the fourth input gear beingfixedly connected to the third input shaft, the fourth shifting gearbeing rotatably mounted on the second output shaft and externallygear-meshed with the fourth input gear, and a seventh gear set includinga fourth input gear and a first idle gear, the fourth input gear fixedlyconnected to the third input shaft, the first idle gear fixedlyconnected to the idle shaft and externally gear-meshed with the fourthinput gear.

The plurality of gear sets may further include an eighth gear setincluding a final reduction gear of a differential, and first and secondoutput gears fixedly connected to the first and second output shaftsrespectively, and externally gear-meshed with the final reduction gear.

The first, second, third, and fourth gear sets may be mounted in alisted order from an opposite side of the engine output shaft on thefirst input shaft and the fifth, sixth, and eighth gear sets may bemounted in a listed order from the opposite side of the engine outputshaft on second output shaft.

The first synchronizer may selectively connect the first shifting gearof the second gear set and the second shifting gear of the third gearset to the first output shaft, and the second synchronizer mayselectively connect the third shifting gear of the fifth gear set andthe fourth shifting gear of the sixth gear set to the second outputshaft.

A power transmission apparatus configured for a vehicle according to anexemplary embodiment of the present invention may realize sixteenshifting stages by combining one simple planetary gear set and twosynchronizers to basic four-speed dual-clutch transmission (DCT)structure.

Furthermore, according to a power transmission apparatus configured fora vehicle according to an exemplary embodiment of the present invention,desired shifting stages may be selected from the sixteen shiftingstages, and therefore, a transmission may be easily optimized forvarious specifications of vehicles, facilitating vehicle-improvement ofpower delivery performance and fuel consumption.

Furthermore, according to a power transmission apparatus configured fora vehicle according to an exemplary embodiment of the present invention,a transmission may be down-sized by employing a simple four-speeddual-clutch transmission (DCT) structure, also improving installability.

Furthermore, effects which may be obtained or expected from exemplaryembodiments of the present invention are directly or suggestivelydescribed in the following detailed description. That is, variouseffects expected from exemplary embodiments of the present inventionwill be described in the following detailed description.

The methods and apparatuses of the present invention have other featuresand advantages which will be apparent from or are set forth in moredetail in the accompanying drawings, which are incorporated herein, andthe following Detailed Description, which together serve to explaincertain principles of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a power transmission apparatus configuredfor a vehicle according to various exemplary embodiments of the presentinvention.

FIG. 2 is a shifting operation chart for a power transmission apparatusconfigured for a vehicle according to various exemplary embodiments ofthe present invention.

FIG. 3 is a schematic view of a power transmission apparatus configuredfor a vehicle according to various exemplary embodiments of the presentinvention.

It may be understood that the appended drawings are not necessarily toscale, presenting a somewhat simplified representation of variousfeatures illustrative of the basic principles of the present invention.The specific design features of the present invention as includedherein, including, for example, specific dimensions, orientations,locations, and shapes will be determined in part by the particularlyintended application and use environment.

In the figures, reference numbers refer to the same or equivalentportions of the present invention throughout the several figures of thedrawing.

DETAILED DESCRIPTION

Reference will now be made in detail to various embodiments of thepresent invention(s), examples of which are illustrated in theaccompanying drawings and described below. While the presentinvention(s) will be described in conjunction with exemplary embodimentsof the present invention, it will be understood that the presentdescription is not intended to limit the present invention(s) to thoseexemplary embodiments. On the other hand, the present invention(s)is/are intended to cover not only the exemplary embodiments of thepresent invention, but also various alternatives, modifications,equivalents and other embodiments, which may be included within thespirit and scope of the present invention as defined by the appendedclaims.

In the following detailed description, only certain exemplaryembodiments of the present invention have been shown and described,simply by way of illustration. As those skilled in the art wouldrealize, the described embodiments may be modified in various differentways, all without departing from the spirit or scope of the presentinvention.

The drawings and description are to be regarded as illustrative innature and not restrictive, and like reference numerals designate likeelements throughout the specification.

In the following description, dividing names of components into first,second and the like is to divide the names because the names of thecomponents are the same as each other and an order thereof is notparticularly limited.

FIG. 1 is a schematic view of a power transmission apparatus accordingto various exemplary embodiments of the present invention.

Referring to FIG. 1, a power transmission apparatus according to variousexemplary embodiments of the present invention includes first, second,and third input shafts IS1, IS2, and IS3, an intermediate shaft CS,first, and second output shafts OS1 and OS2, an idle shaft IDS, aplanetary gear set PG, first, second, third, fourth, fifth, sixth,seventh and eighth gear sets GT1, GT2, GT3, GT4, GT5, GT6, GT7 and GT8)first, and second synchronizers SM1 and SM2, and first, second, third,and fourth clutches CL1, CL2, CL3, and CL4.

A power source of the power transmission apparatus may be various typesof a known engine ENG, such as a gasoline engine or a diesel engine.

The first, second, and third input shafts IS1, IS2, and IS3 are mountedat a same axis. The first input shaft IS1 is an input member, andfixedly connected to an engine output shaft EOS (or a crankshaft) of anengine ENG, and a first input gear IG1 is fixedly mounted on an externalcircumference of the first input shaft IS1.

The first input shaft IS1 may receive the torque of the engine outputshaft EOS through a torque converter.

The second input shaft IS2 is formed as a hollow shaft, mounted coaxialwith and external to the first input shaft IS1 without rotationalinterference therebetween, and selectively connectable to the firstinput shaft IS1.

The second input shaft IS2 is external to the first input shaft IS1excluding an end portion of the first input shaft IS1, and second andthird input gears IG2 and IG3 are fixedly mounted to the second inputshaft IS2 at locations toward the excluded end portion of the firstinput shaft IS1.

The third input shaft IS3 is formed as a hollow shaft, mounted coaxialwith and external to the second input shaft IS2 without rotationalinterference therebetween, and selectively connectable to the secondinput shaft IS2.

The third input shaft IS3 is external to the second input shaft IS2excluding an end portion of the second input shaft IS2, and fourth inputgear IG4 is fixedly mounted to the third input shaft IS3.

The intermediate shaft CS is mounted in parallel with the first, second,and third input shafts IS1, IS2, and IS3, and is fixedly mounted with afirst external gear EG1 which is externally gear-meshed with the firstinput gear IG1 at the first input shaft IS1.

The first output shaft OS1 is an output element, and mounted in parallelwith the first, second, and third input shafts IS1, IS2, and IS3. Firstand second shifting gears SG1 and SG2 are rotatably mounted on the firstoutput shaft OS1, and are externally gear-meshed with the second andthird input gears IG2 and IG3 on the second input shaft IS2.

The first output shaft OS1 receives a shifted driving torque through twogear sets and transmits the shifted driving torque to a differentialDIFF through a first output gear OG1 and a final reduction gear FDG.

The second output shaft OS2 is an output element, and mounted inparallel with the first, second, and third input shafts IS1, IS2, andIS3. Third and fourth shifting gears SG3 and SG4 are rotatably mountedon the second output shaft OS2 and the fourth shifting gear SG4 isexternally gear-meshed with the fourth input gear IG4 on the third inputshaft IS3.

The second output shaft OS2 receives a shifted driving torque throughtwo gear sets and transmits the shifted driving torque to thedifferential DIFF through a second output gear OG2 and the finalreduction gear FDG.

The idle shaft IDS is mounted in parallel with the second output shaftOS2, and first and second idle gears IDG1 and IDG2 are fixedly connectedto the idle shaft IDS.

The first idle gear IDG1 is externally gear-meshed with fourth inputgear IG4 on the third input shaft IS3 and the second idle gear IDG2 isexternally gear-meshed with the third shifting gear SG3 on the secondoutput shaft OS2.

The idle shaft IDS decelerates the rotation speed of the fourth shiftinggear SG4 and transfers it to the third shifting gear SG3.

The planetary gear set PG is mounted on an axis of the intermediateshaft CS. The planetary gear set PG merely outputs a torque receivedfrom the first input shaft IS1, or outputs a shifted torque obtainedfrom torques from the first input shaft IS1 and the second and thirdinput shafts IS2 and IS3.

In more detail, the planetary gear set PG may receive torques from thefirst input shaft IS1 and the second input shaft IS2, outputting ashifted torque to the third input shaft IS3, or may receive torques fromthe first input shaft IS1 and the third input shaft IS3 therebyoutputting a shifted torque to the second input shaft IS2.

The planetary gear set PG is a single pinion planetary gear set, andincludes a sun gear S, a planet carrier PC rotatably supporting aplurality of pinion gear P externally gear-meshed with the sun gear S,and a ring gear R internally gear-meshed with the plurality of piniongear P engaged with the sun gear S. The sun gear S acts as a firstrotation element N1, the planet carrier PC acts as a second rotationelement N2, and the ring gear R acts as a third rotation element N3.

The first and third rotation elements N1 and N3 are selectivelyconnectable to the intermediate shaft CS, respectively, and the firstand second rotation elements Ni and N2 are respectively connected to thethird and second input shafts IS3 and IS2 through corresponding gearsets.

The eight gear sets GT1 to GT8 are hereinafter described in detail.

The first gear set GT1 includes a first input gear IG1 and a firstexternal gear EG1. The first input gear IG1 is fixedly connected to thefirst input shaft IS1, and the first external gear EG1 is fixedlyconnected to the intermediate shaft CS and externally gear-meshed withthe first input gear IG1.

In the first gear set GT1 of various exemplary embodiments of thepresent invention, the first external gear EG1 may be selectivelyconnectable to the first rotation element N1 (sun gear S) and the thirdrotation element N3 (ring gear R) of the planetary gear set PG, throughthe intermediate shaft CS.

The second gear set GT2 includes a second input gear IG2 and a firstshifting gear SG1. The second input gear IG2 is fixedly connected to thesecond input shaft IS2, and the first shifting gear SG1 is rotatablymounted on the first output shaft OS1 and externally gear-meshed withthe second input gear IG2.

The third gear set GT3 includes a second external gear EG2, the thirdinput gear IG3, and the second shifting gear SG2. The second externalgear EG2 is fixedly connected to the second rotation element N2 (planetcarrier PC) of the planetary gear set PG. The third input gear IG3 isfixedly connected to second input shaft IS2 and externally gear-meshedwith the second external gear EG2. The second shifting gear SG2 isrotatably mounted on the first output shaft OS1 and externallygear-meshed with the third input gear IG3.

The fourth gear set GT4 includes a third external gear EG3 and a fourthinput gear IG4. The third external gear EG3 is fixedly connected to thefirst rotation element N1 (sun gear S) of the planetary gear set PG. Thefourth input gear IG4 is fixedly connected to the third input shaft IS3and externally gear-meshed with the third external gear EG3.

The fifth gear set GT5 includes the third shifting gear SG3 and thesecond idle gear IDG2. The third shifting gear SG3 is rotatably mountedon the second output shaft OS2. The second idle gear IDG2 is fixedlyconnected to idle shaft IDS and externally gear-meshed with the thirdshifting gear SG3.

The sixth gear set GT6 includes the fourth input gear IG4 and the fourthshifting gear SG4. The fourth input gear IG4 is fixedly connected tothird input shaft IS3. The fourth shifting gear SG4 is rotatably mountedon the second output shaft OS2 and externally gear-meshed with thefourth input gear IG4.

The seventh gear set GT7 includes the fourth input gear IG4 and thefirst idle gear IDG1. The fourth input gear IG4 is fixedly connected tothird input shaft IS3 and the first idle gear IDG1 is fixedly connectedto the idle shaft IDS and externally gear-meshed with the fourth inputgear IG4.

The fourth input gear IG4 is formed to have a wide gear width so thatthe fourth shifting gear SG4 and the first idle gear IDG1 may be engagedthereto adjacent each other.

The eighth gear set GT8 includes the final reduction gear FDG of thedifferential DIFF, and the first and second output gears OG1 and OG2.The first and second output gears OG1 and OG2 are fixedly connected tothe first and second output shafts OS1 respectively and externallygear-meshed with the final reduction gear FDG.

The first, second, third, and fourth gear sets GT1, GT2, GT3 and GT4 aremounted in a listed order from an opposite side of the engine outputshaft on the first input shaft IS1 and the fifth, sixth, and eighth gearsets GT5, GT6, and GT8 are mounted in a listed order from the oppositeside of the engine output shaft on second output shaft OS2.

The first, second, third, and fourth shifting gears SG1, SG2, SG3, andSG4 rotatably mounted on the first and second output shafts OS1 and OS2are selectively connectable to the first and second output shafts OS1and OS2 by first and second synchronizers SM1 and SM2.

The first synchronizer SM1 selectively synchronizes the first shiftinggear SG1 and the second shifting gear SG2 to the first output shaft OS1,and the second synchronizer SM2 selectively synchronizes the thirdshifting gear SG3 and the fourth shifting gear SG4 to the second outputshaft OS2.

The first and second synchronizers SM1 and SM2 may be formed as a knownscheme, and first and second sleeves SLE1 and SLE2 applied to the firstand second synchronizers SM1 and SM2 may be operated by actuators whichmay be controlled by a transmission control unit.

Gear ratios of the first to eighth gear sets GT1 to GT8 may be set inconsideration of design requirements of a transmission.

Furthermore, engagement elements of first to fourth clutches CL1, CL2,CL3, and CL4 are mounted between rotation members such as variousshafts.

The four clutches CL1 to CL4 are mounted as follows.

The first clutch CL1 is mounted between the first input shaft IS1 andthe second input shaft IS2, and selectively connects the first inputshaft IS1 and the second input shaft IS2.

The second clutch CL2 is mounted between the first input shaft IS1 andthe third input shaft IS3, and selectively connects the first inputshaft IS1 and the third input shaft IS3.

The third clutch CL3 is mounted between the intermediate shaft CS andthe third rotation element N3 (ring gear R) of the planetary gear setPG, and selectively connects the intermediate shaft CS and the ring gearR.

The fourth clutch CL4 is mounted between the intermediate shaft CS andthe first rotation element N1 (sun gear S) of the planetary gear set PG,and selectively connects the intermediate shaft CS and the sun gear S.

The engagement elements of the first, second, third, and fourth clutchesC1, C2, C3, and C4 may be realized as multi-plate hydraulic pressurefriction devices that are frictionally engaged by hydraulic pressure,however, it may not be understood to be limited thereto, since variousother configuration that are electrically controllable may be available.

In the disclosure, when two or more members are described to be “fixedlyconnected”, where the member may be any of a shaft, an input shaft, anoutput shaft, a rotation member, and a transmission housing, it meansthat the fixedly connected members always rotate at a same speed. Thatis, rotation elements and/or shafts fixedly interconnected rotate in asame rotating direction and at a same rotation speed.

When two or more members are described to be “selectively connectable”by an engagement element, it means that the selectively connectablemembers rotate separately when the engagement element is not engaged,and rotates at a same speed when the engagement element is engaged. Itmay be understood that in the case that a member is “selectivelyconnectable” with a transmission housing by an engagement element, themember may be stationary when the engagement element is engaged.

FIG. 2 is a shifting operation chart for a power transmission apparatusaccording to various exemplary embodiments of the present invention, andthe power transmission apparatus according to various exemplaryembodiments performs shifting operation as follows.

A power transmission apparatus according to various exemplaryembodiments may realize a plurality of shifting stages by selectionoperation of the engagement elements of the four clutches CL1 to CL4 andthe two synchronizers SM1 and SM2.

The exemplary power transmission apparatus may realize sixteen shiftingstages that include two shifting stages by the operation of the firstsynchronizer SM1 under the simultaneous operation of the second andthird clutches CL2 and CL3, two shifting stages by the operation of thesecond synchronizer SM2 under the simultaneous operation of the firstand third clutches CL1 and CL3, two shifting stages by the operation ofthe first synchronizer SM1 under the operation of the first clutch CL1,two shifting stages by the operation of the second synchronizer SM2under the operation of the second clutch CL2, four shifting stages bythe operation of the first synchronizer SM1 or second synchronizer SM2under the simultaneous operation of the third and fourth clutches CL3and CL4, and four shifting stages by the operation of the first andsecond synchronizers SM1 and SM2 under the operation of the third clutchCL3.

A power transmission apparatus according to various exemplaryembodiments may achieve a desired number of shifting stages selectedfrom the available sixteen shifting stages depending on desiredcharacteristic of a transmission.

[First Shift-Stage]

In the first shift-stage, while the second and third clutches CL2 andCL3 are under operation, the first synchronizer SM1 is controlled tosynchronously connect the first shifting gear SG1 and the first outputshaft OS1.

Accordingly, the torque of the engine ENG is input to the first rotationelement N1 of the planetary gear set PG by the operation of the secondclutch CL2 through the first input shaft IS1, the second clutch CL2, thethird input shaft IS3, and the fourth gear set GT4, and simultaneouslyinput to the third rotation element N3 of the planetary gear set PG bythe operation of the third clutch CL3 through the first input shaft IS1,the first gear set GT1, and the third clutch CL3.

In the planetary gear set PG, the first rotation element Ni receives atorque according to the gear ratio of the fourth gear set GT4, and thethird rotation element N3 receives a torque according to the gear ratioof the first gear set GT1.

The torques of the first and third input shafts IS1 and IS3 are shiftedin the planetary gear set PG according to the rotation speed differenceof the third and first rotation elements N3 and Ni thereby outputtingthe shifted torque to the second rotation element N2, and the torque ofthe second rotation element N2 is shifted while passing through thethird gear set GT3, the second gear set GT2, the first output shaft OS1,the first output gear OG1, and the final reduction gear FDG to betransmitted to the differential DIFF.

In the first shift-stage, torques of the first and third input shaftsIS1 and IS3 are primarily shifted by the gear ratios of the fourth andfirst gear sets GT4 and GT1 and by the rotation speed difference of thethird and first rotation elements N3 and Ni in the planetary gear setPG, and secondarily shifted by the gear ratios of the third and secondgear sets GT3 and GT2, afterwards being transmitted to the first outputshaft OS1.

In the instant case, the second synchronizer SM2 is maintained to aneutral state, and the torque of the third input shaft IS3 is not passedto the second output shaft OS2 through the sixth and seventh gear setsGT6 and GT7.

[Second Shift-Stage]

In the second shift-stage, while the second and third clutches CL2 andCL3 are under operation, the first synchronizer SM1 is controlled tosynchronously connect the second shifting gear SG2 and the first outputshaft OS1.

Accordingly, the torque of the engine ENG is input to the first rotationelement Ni of the planetary gear set PG by the operation of the secondclutch CL2 through the first input shaft IS1, the second clutch CL2, thethird input shaft IS3, and the fourth gear set GT4, and simultaneouslyinput to the third rotation element N3 of the planetary gear set PG bythe operation of the third clutch CL3 through the first input shaft IS1,the first gear set GT1, and the third clutch CL3.

In the planetary gear set PG, the first rotation element Ni receives atorque according to the gear ratio of the fourth gear set GT4, and thethird rotation element N3 receives a torque according to the gear ratioof the first gear set GT1.

The torques of the first and third input shafts IS1 and IS3 are shiftedin the planetary gear set PG according to the rotation speed differenceof the third and first rotation elements N3 and Ni thereby outputtingthe shifted torque to the second rotation element N2, and the torque ofthe second rotation element N2 is shifted while passing through thethird gear set GT3, the first output shaft OS1, the first output gearOG1, and the final reduction gear FDG to be transmitted to thedifferential DIFF.

In the first shift-stage, torques of the first and third input shaftsIS1 and IS3 are primarily shifted by the gear ratios of the fourth andfirst gear sets GT4 and GT1 and by the rotation speed difference of thethird and first rotation elements N3 and Ni in the planetary gear setPG, and secondarily shifted by the gear ratio of the third gear set GT3,afterwards being transmitted to the first output shaft OS1.

In the instant case, the second synchronizer SM2 is maintained to aneutral state, and the torque of the third input shaft IS3 is not passedto the second output shaft OS2 through the sixth and seventh gear setsGT6 and GT7.

[Third Shift-Stage]

In the third shift-stage, while the first and third clutches CL1 and CL3are under operation, the second synchronizer SM2 is controlled tosynchronously connect the third shifting gear SG3 and the second outputshaft OS2.

Accordingly, the torque of the engine ENG is input to the secondrotation element N2 of the planetary gear set PG by the operation of thefirst clutch CL1 through the first input shaft IS1, the first clutchCL1, the second input shaft IS2, and the third gear set GT3, andsimultaneously input to the third rotation element N3 of the planetarygear set PG by the operation of the third clutch CL3 through the firstinput shaft IS1, the first gear set GT1, and the third clutch CL3.

In the planetary gear set PG, the second rotation element N2 receives atorque according to the gear ratio of the first gear set GT1, and thethird rotation element N3 receives a torque according to the gear ratioof the first gear set GT1.

The torques of the first and second input shafts IS1 and IS2 are shiftedin the planetary gear set PG according to the rotation speed differenceof the third and second rotation elements N3 and N2 thereby outputtingthe shifted torque to the first rotation element N1, and the torque ofthe first rotation element Ni is shifted while passing through thefourth, seventh, and fifth gear sets GT4, GT7 and GT5, the second outputshaft OS2, the second output gear OG2, and the final reduction gear FDGto be transmitted to the differential DIFF.

In the third shift-stage, torques of the first and second input shaftsIS1 and IS2 are primarily shifted by the gear ratios of the first andthird gear sets GT1 and GT3 and by the rotation speed difference of thethird and second rotation elements N3 and N2 in the planetary gear setPG, and secondarily shifted by the gear ratios of the fourth, seventh,and fifth gear sets GT4, GT7 and GT5, afterwards being transmitted tothe second output shaft OS2.

In the instant case, the first synchronizer SM1 is maintained to aneutral state, and the torque of the second input shaft IS2 is notpassed to the first output shaft OS1 through the second gear set GT2 andthe third gear set GT3.

[Fourth Shift-Stage]

In the fourth shift-stage, while the first and third clutches CL1 andCL3 are under operation, the second synchronizer SM2 is controlled tosynchronously connect the fourth shifting gear SG4 and the second outputshaft OS2.

Accordingly, the torque of the engine ENG is input to the secondrotation element N2 of the planetary gear set PG by the operation of thefirst clutch CL1 through the first input shaft IS1, the first clutchCL1, the second input shaft IS2, and the third gear set GT3, andsimultaneously input to the third rotation element N3 of the planetarygear set PG by the operation of the third clutch CL3 through the firstinput shaft IS1, the first gear set GT1, and the third clutch CL3.

In the planetary gear set PG, the second rotation element N2 receives atorque according to the gear ratio of the third gear set GT3, and thethird rotation element N3 receives a torque according to the gear ratioof the first gear set GT1.

The torques of the first and second input shafts IS1 and IS2 are shiftedin the planetary gear set PG according to the rotation speed differenceof the third and second rotation elements N3 and N2 thereby outputtingthe shifted torque to the first rotation element N1, and the torque ofthe first rotation element N1 is shifted while passing through thefourth and sixth gear sets GT4 and GT6, the second output shaft OS2, thesecond output gear OG2, and the final reduction gear FDG to betransmitted to the differential DIFF.

In the fourth shift-stage, torques of the first and second input shaftsIS1 and IS2 are primarily shifted by the gear ratios of the first andthird gear sets GT1 and GT3 and by the rotation speed difference of thethird and second rotation elements N3 and N2 in the planetary gear setPG, and secondarily shifted by the gear ratios of the fourth and sixthgear sets GT4 and GT6, afterwards being transmitted to the second outputshaft OS2.

In the instant case, the first synchronizer SM1 is maintained to aneutral state, and the torque of the second input shaft IS2 is notpassed to the first output shaft OS1 through the second gear set GT2 andthe third gear set GT3.

[Fifth Shift-Stage]

In the fifth shift-stage, while the first clutch CL1 is under operation,the first synchronizer SM1 is controlled to synchronously connect thefirst shifting gear SG1 and the first output shaft OS1.

Accordingly, by the operation of the first clutch CL1, the torque of theengine ENG is shifted while passing through the first input shaft IS1,the first clutch CL1, the second input shaft IS2, the second gear setGT2, the first output shaft OS1, the first output gear OG1, and thefinal reduction gear FDG to be transmitted to the differential DIFF.

In the fifth shift-stage, the torque of the first input shaft IS1 isshifted by the gear ratio of the second gear set GT2, and transmitted tothe first output shaft OS1.

In the instant case, the operation of the second synchronizer SM2 tosynchronously connect the third shifting gear SG3 or fourth shiftinggear SG4 to the second output shaft OS2 does not affect the shiftingoperation.

[Sixth Shift-Stage]

In the sixth shift-stage, while the first clutch CL1 is under operation,the first synchronizer SM1 is controlled to synchronously connect thesecond shifting gear SG2 and the first output shaft OS1.

Accordingly, by the operation of the first clutch CL1, the torque of theengine ENG is shifted while passing through the first input shaft IS1,the first clutch CL1, the second input shaft IS2, the third gear setGT3, the first output shaft OS1, the first output gear OG1, and thefinal reduction gear FDG to be transmitted to the differential DIFF.

In the sixth shift-stage, the torque of the first input shaft IS1 isshifted by the gear ratio of the third gear set GT3, and transmitted tothe first output shaft OS1.

In the instant case, the operation of the second synchronizer SM2 tosynchronously connect the third shifting gear SG3 or fourth shiftinggear SG4 to the second output shaft OS2 does not affect the shiftingoperation.

[Seventh Shift-Stage]

In the seventh shift-stage, while the second clutch CL2 is underoperation, the second synchronizer SM2 is controlled to synchronouslyconnect the third shifting gear SG3 and the second output shaft OS2.

Accordingly, by the operation of the second clutch CL2, the torque ofthe engine ENG is shifted while passing through the first input shaftIS1, the second clutch CL2, the third input shaft IS3, the seventh andfifth gear sets GT7 and GT5, the second output shaft OS2, the secondoutput gear OG2 and the final reduction gear to be transmitted to thedifferential DIFF.

In the seventh shift-stage, the torque of the first input shaft IS1 isshifted by the gear ratio of the seventh and fifth gear sets GT7 andGT5, and transmitted to the second output shaft OS2.

In the instant case, the operation of the first synchronizer SM1 tosynchronously connect the first shifting gear SG1 or second shiftinggear SG2 to the first output shaft OS1 does not affect the shiftingoperation.

[Eighth Shift-Stage]

In the eighth shift-stage, while the second clutch CL2 is underoperation, the second synchronizer SM2 is controlled to synchronouslyconnect the fourth shifting gear SG4 and the second output shaft OS2.

Accordingly, by the operation of the second clutch CL2, the torque ofthe engine ENG is shifted while passing through the first input shaftIS1, the second clutch CL2, the third input shaft IS3, the sixth gearset GT6, the second output shaft OS2, the second output gear OG2, andthe final reduction gear FDG to be transmitted to the differential DIFF.

In the eighth shift-stage, the torque of the first input shaft IS1 isshifted by the gear ratio of the sixth gear set GT6, and transmitted tothe second output shaft OS2.

In the instant case, the operation of the first synchronizer SM1 tosynchronously connect the first shifting gear SG1 or second shiftinggear SG2 to the first output shaft OS1 does not affect the shiftingoperation.

[Ninth Shift-Stage]

In the ninth shift-stage, while the third and fourth clutches CL3 andCL4 are under operation, the first synchronizer SM1 is controlled tosynchronously connect the first shifting gear SG1 and the first outputshaft OS1.

Accordingly, the torque of the engine ENG is input to the third rotationelement N3 of the planetary gear set PG by the operation of the thirdclutch CL3 through the first input shaft IS1, the first gear set GT1,and the third clutch CL3, and simultaneously input to the first rotationelement Ni of the planetary gear set PG by the operation of the fourthclutch CL4 through the first input shaft IS1, the first gear set GT1,and the fourth clutch CL4.

Accordingly, the planetary gear set PG integrally rotates by receivingthe same torque of the first input shaft IS1 through the first and thirdrotation elements Ni and N3, and merely transmits the torque of thefirst and third rotation elements Ni and N3 to the first and secondrotation elements N1 and N2.

The torque of the second rotation element N2 is shifted while passingthrough the third gear set GT3, the second gear set GT2, the firstoutput shaft OS1, the first output gear OG1, and the final reductiongear FDG to be transmitted to the differential DIFF.

In the ninth shift-stage, the torque of the first input shaft IS1 isshifted by the gear ratio of the first, third, and second gear sets GT1,GT3, and GT2, and transmitted to the first output shaft OS1.

Since the second synchronizer SM2 is maintained to a neutral state, thetorque output from the second rotation element N2 of the planetary gearset PG is not transmitted to the second output shaft OS2 and does notaffect the shifting operation.

[Tenth Shift-Stage]

In the tenth shift-stage, while the third and fourth clutches CL3 andCL4 are under operation, the first synchronizer SM1 is controlled tosynchronously connect the second shifting gear SG2 and the first outputshaft OS1.

Accordingly, the torque of the engine ENG is input to the third rotationelement N3 of the planetary gear set PG by the operation of the thirdclutch CL3 through the first input shaft IS1, the first gear set GT1,and the third clutch CL3, and simultaneously input to the first rotationelement Ni of the planetary gear set PG by the operation of the fourthclutch CL4 through the first input shaft IS1, the first gear set GT1,and the fourth clutch CL4.

Accordingly, the planetary gear set PG integrally rotates by receivingthe same torque of the first input shaft IS1 through the first and thirdrotation elements Ni and N3, and merely transmits the torque of thefirst and third rotation elements Ni and N3 to the first and secondrotation elements Ni and N2.

The torque of the second rotation element N2 is shifted while passingthrough the third gear set GT3, the first output shaft OS1, the firstoutput gear OG1, and the final reduction gear FDG to be transmitted tothe differential DIFF.

In the tenth shift-stage, the torque of the first input shaft IS1 isshifted by the gear ratios of the first gear set GT1 and the third gearset GT3, and transmitted to the first output shaft OS1.

Since the second synchronizer SM2 is maintained to a neutral state, thetorque output from the first rotation element Ni of the planetary gearset PG is not transmitted to the second output shaft OS2 and does notaffect the shifting operation.

[Eleventh Shift-Stage]

In the eleventh shift-stage, while the third and fourth clutches CL3 andCL4 are under operation, the second synchronizer SM2 is controlled tosynchronously connect the third shifting gear SG3 and the second outputshaft OS2.

Accordingly, the torque of the engine ENG is input to the third rotationelement N3 of the planetary gear set PG by the operation of the thirdclutch CL3 through the first input shaft IS1, the first gear set GT1,and the third clutch CL3, and simultaneously input to the first rotationelement Ni of the planetary gear set PG by the operation of the fourthclutch CL4 through the first input shaft IS1, the first gear set GT1,and the fourth clutch CL4.

Accordingly, the planetary gear set PG integrally rotates by receivingthe same torque of the first input shaft IS1 through the first and thirdrotation elements Ni and N3, and merely transmits the torque of thefirst and third rotation elements Ni and N3 to the first and secondrotation elements Ni and N2.

The torque of the first rotation element Ni is shifted while passingthrough the fourth, seventh, and fifth gear set GT4, GT7, and GT5, thesecond output shaft OS2, and second output gear OG2, and the finalreduction gear FDG to be transmitted to the differential DIFF.

In the eleventh shift-stage, the torque of the first input shaft IS1 isshifted by the gear ratios of the first gear set GT1, the fourth,seventh, and fifth gear sets GT4, GT7, and GT5, and transmitted to thefirst output shaft OS1.

Since the first synchronizer SM1 is maintained to a neutral state, thetorque output from the second rotation element N2 of the planetary gearset PG is not transmitted to the first output shaft OS1 and does notaffect the shifting operation.

[Twelfth Shift-Stage]

In the twelfth shift-stage, while the third and fourth clutches CL3 andCL4 are under operation, the second synchronizer SM2 is controlled tosynchronously connect the fourth shifting gear SG4 and the second outputshaft OS2.

Accordingly, the torque of the engine ENG is input to the third rotationelement N3 of the planetary gear set PG by the operation of the thirdclutch CL3 through the first input shaft IS1, the first gear set GT1,and the third clutch CL3, and simultaneously input to the first rotationelement Ni of the planetary gear set PG by the operation of the fourthclutch CL4 through the first input shaft IS1, the first gear set GT1,and the fourth clutch CL4.

Accordingly, the planetary gear set PG integrally rotates by receivingthe same torque of the first input shaft IS1 through the first and thirdrotation elements Ni and N3, and merely transmits the torque of thefirst and third rotation elements Ni and N3 to the first and secondrotation elements Ni and N2.

The torque of the first rotation element Ni is shifted while passingthrough the fourth and sixth gear set GT4 and GT6, the second outputshaft OS2, and second output gear OG2, and the final reduction gear FDGto be transmitted to the differential DIFF.

In the twelfth shift-stage, the torque of the first input shaft IS1 isshifted by the gear ratios of the first, fourth, and sixth gear setsGT1, GT4, and GT6, and transmitted to the second output shaft OS2.

Since the first synchronizer SM1 is maintained to a neutral state, thetorque output from the second rotation element N2 of the planetary gearset PG is not transmitted to the first output shaft OS1 and does notaffect the shifting operation.

[Thirteenth Shift-Stage]

In the thirteenth shift-stage, while the third clutch CL3 is underoperation, the first synchronizer SM1 is controlled to synchronouslyconnect the first shifting gear SG1 and the first output shaft OS1, andthe second synchronizer SM2 is controlled to synchronously connect thethird shifting gear SG3 and the second output shaft OS2.

Accordingly, by the operation of the first synchronizer SM1, the secondrotation element N2 of the planetary gear set PG is connected to thefirst output shaft OS1 through the third gear set GT3 and the secondgear set GT2, and by the operation of the second synchronizer SM2, thefirst rotation element Ni of the planetary gear set PG is connected tothe second output shaft OS2 through the fourth, seventh, and fifth gearset GT4, GT7, and GT5. in the instant state, the torque of the engineENG is input to the third rotation element N3 of the planetary gear setPG through the first input shaft IS1, the first gear set GT1, and thethird clutch CL3.

As a result, the first and second rotation elements Ni and N2 of theplanetary gear set PG form a closed torque loop together with the firstand second output shafts OS1 and 052 and the final reduction gear FDG.In the instant case, the first rotation element Ni receives a shiftedtorque according to the gear ratios of the fourth, seventh and fifthgear sets GT4, GT7, and GT5, and the second rotation element N2 receivesa shifted torque according to the gear ratios of the third and secondgear sets GT3 and GT2. Therefore, the torque input to the third rotationelement N3 is shifted and transmitted through the first and secondoutput shafts OS1 and OS2, the first and second output gears OG1 andOG2, and the final reduction gear FDG and to the differential DIFF.

[Fourteenth Shift-Stage]

In the fourteenth shift-stage, while the third clutch CL3 is underoperation, the first synchronizer SM1 is controlled to synchronouslyconnect the first shifting gear SG1 and the first output shaft OS1, andthe second synchronizer SM2 is controlled to synchronously connect thefourth shifting gear SG4 and the second output shaft OS2.

Accordingly, by the operation of the first synchronizer SM1, the secondrotation element N2 of the planetary gear set PG is connected to thefirst output shaft OS1 through the third gear set GT3 and the secondgear set GT2, and by the operation of the second synchronizer SM2, thefirst rotation element Ni of the planetary gear set PG is connected tothe second output shaft OS2 through the fourth and sixth gear sets GT4and GT6, in the instant state in the instant state, the torque of theengine ENG is input to the third rotation element N3 of the planetarygear set PG through the first input shaft IS1, the first gear set GT1,and the third clutch CL3.

As a result, the first and second rotation elements Ni and N2 of theplanetary gear set PG form a closed torque loop together with the firstand second output shafts OS1 and 052 and the final reduction gear FDG.In the instant case, the first rotation element Ni receives a shiftedtorque according to the gear ratios of the fourth and sixth gear setsGT4 and GT6, and the second rotation element N2 receives a shiftedtorque according to the gear ratios of the third and second gear setsGT3 and GT2. Therefore, the torque input to the third rotation elementN3 is shifted and transmitted through the first and second output shaftsOS1 and OS2, the first and second output gears OG1 and OG2, and thefinal reduction gear FDG and to the differential DIFF.

[Fifteenth Shift-Stage]

In the fifteenth shift-stage, while the third clutch CL3 is underoperation, the first synchronizer SM1 is controlled to synchronouslyconnect the second shifting gear SG2 and the first output shaft OS1, andthe second synchronizer SM2 is controlled to synchronously connect thethird shifting gear SG3 and the second output shaft OS2.

Accordingly, by the operation of the first synchronizer SM1, the secondrotation element N2 of the planetary gear set PG is connected to thefirst output shaft OS1 through the third gear set GT3, and by theoperation of the second synchronizer SM2, the first rotation element Niof the planetary gear set PG is connected to the second output shaft OS2through the fourth, seventh, and fifth gear set GT4, GT7, and GT5. inthe instant state, the torque of the engine ENG is input to the thirdrotation element N3 of the planetary gear set PG through the first inputshaft IS1, the first gear set GT1, and the third clutch CL3.

As a result, the first and second rotation elements Ni and N2 of theplanetary gear set PG form a closed torque loop together with the firstand second output shafts OS1 and OS2 and the final reduction gear FDG.In the instant case, the first rotation element Ni receives a shiftedtorque according to the gear ratios of the fourth, seventh and fifthgear sets GT4, GT7, and GT5, and the second rotation element N2 receivesa shifted torque according to the gear ratio of the third gear set GT3.Therefore, the torque input to the third rotation element N3 is shiftedand transmitted through the first and second output shafts OS1 and OS2,the first and second output gears OG1 and OG2, and the final reductiongear FDG and to the differential DIFF.

[Sixteenth Shift-Stage]

In the sixteenth shift-stage, while the third clutch CL3 is underoperation, the first synchronizer SM1 is controlled to synchronouslyconnect the second shifting gear SG2 and the first output shaft OS1, andthe second synchronizer SM2 is controlled to synchronously connect thefourth shifting gear SG4 and the second output shaft OS2.

Accordingly, by the operation of the first synchronizer SM1, the secondrotation element N2 of the planetary gear set PG is connected to thefirst output shaft OS1 through the third gear set GT3, and by theoperation of the second synchronizer SM2, the first rotation element Niof the planetary gear set PG is connected to the second output shaft OS2through the fourth and sixth gear sets GT4 and GT6, in the instant statein the instant state, the torque of the engine ENG is input to the thirdrotation element N3 of the planetary gear set PG through the first inputshaft IS1, the first gear set GT1, and the third clutch CL3.

As a result, the first and second rotation elements Ni and N2 of theplanetary gear set PG form a closed torque loop together with the firstand second output shafts OS1 and 052 and the final reduction gear FDG.In the instant case, the first rotation element Ni receives a shiftedtorque according to the gear ratios of the fourth and sixth sets GT4 andGT6, and GT5, and the second rotation element N2 receives a shiftedtorque according to the gear ratio of the third gear set GT3. Therefore,the torque input to the third rotation element N3 is shifted andtransmitted through the first and second output shafts OS1 and OS2, thefirst and second output gears OG1 and OG2, and the final reduction gearFDG and to the differential DIFF.

The Gear ratios of the first to eighth gear sets GT1 to GT8 may be setin consideration of design requirements of a transmission.

For example, gear ratios of the respective gear sets GT1 to GT8 may beformed as follows.

The gear ratio of the first external gear EG1 to the first input gearIG1 in the first gear set GT1 may be 0.250.

The gear ratio of the first shifting gear SG1 to the second input gearIG2 in the second gear set GT2 may be 2.500.

The gear ratio of the third input gear IG3 to the second external gearEG2 in the third gear set GT3 may be 0.450.

The gear ratio of the second shifting gear SG2 to the third input gearIG3 in the third gear set GT3 may be 0.724.

The gear ratio of the third external gear EG3 to the fourth input gearIG4 in the fourth gear set GT4 may be 0.400,

The gear ratio of the third shifting gear SG3 to the second idle gearIDG2 in the fifth gear set GT2 may be 1.913,

The gear ratio of the fourth shifting gear SG4 to the fourth input gearIG4 in the sixth gear set GT6 may be 0.913.

The gear ratio of the first idle gear IDG1 to the fourth input gear IG4in the seventh gear set GT7 may be 2.091.

The gear ratio of the final reduction gear FDG to the first output gearOG1 (or second output gear OG2) in the eighth gear set GT8 may be 3.667.

The gear ratio of the planetary gear set PG may be 1.400.

As a result, a transmission of desired number of shifting stages withdesired gear ratio may be designed with reference to the gear ratios ofthe sixteen shifting stages. For example, as shown in FIG. 2, atransmission of forward nine speeds and one reverse speed may bedesigned using first, second, fifth, sixth, seventh, eighth, ninth,tenth, thirteenth and sixteenth shifting stages.

FIG. 3 is a schematic view of a power transmission apparatus accordingto various exemplary embodiments of the present invention.

Referring to FIG. 3, in various exemplary embodiments of the presentinvention, the fourth clutch CL4 is mounted between the intermediateshaft CS and the second rotation element N2 (planet carrier PC) of theplanetary gear set PG, in comparison with the various exemplaryembodiments of FIG. 1 where the fourth clutch CL4 is mounted between theintermediate shaft CS and the first rotation element N1 (sun gear S) ofthe planetary gear set PG.

The various exemplary embodiments of FIG. 3 only differ from the variousexemplary embodiments of FIG. 1 in the location of the fourth clutchCL4, providing the same shafting operation and effect, which istherefore not described in further detail.

As described above, a power transmission apparatus configured for avehicle according to an exemplary embodiment of the present inventionmay realize sixteen shifting stages by combining one simple planetarygear set and two synchronizers to basic four-speed dual-clutchtransmission (DCT) structure.

Furthermore, according to a power transmission apparatus configured fora vehicle according to an exemplary embodiment of the present invention,desired shifting stages may be selected from the sixteen shiftingstages, and therefore, a transmission may be easily optimized forvarious specifications of vehicles, facilitating vehicle-improvement ofpower delivery performance and fuel consumption.

Furthermore, according to a power transmission apparatus configured fora vehicle according to an exemplary embodiment of the present invention,a transmission may be down-sized by employing a simple four-speeddual-clutch transmission (DCT) structure, also improving installability.

For convenience in explanation and accurate definition in the appendedclaims, the terms “upper”, “lower”, “inner”, “outer”, “up”, “down”,“upwards”, “downwards”, “front”, “rear”, “back”, “inside”, “outside”,“inwardly”, “outwardly”, “internal”, “external”, “inner”, “outer”,“forwards”, and “backwards” are used to describe features of theexemplary embodiments with reference to the positions of such featuresas displayed in the figures. It will be further understood that the term“connect” or its derivatives refer both to direct and indirectconnection.

The foregoing descriptions of specific exemplary embodiments of thepresent invention have been presented for purposes of illustration anddescription. They are not intended to be exhaustive or to limit thepresent invention to the precise forms disclosed, and obviously manymodifications and variations are possible in light of the aboveteachings. The exemplary embodiments were chosen and described toexplain certain principles of the present invention and their practicalapplication, to enable others skilled in the art to make and utilizevarious exemplary embodiments of the present invention, as well asvarious alternatives and modifications thereof. It is intended that thescope of the present invention be defined by the Claims appended heretoand their equivalents.

What is claimed is:
 1. A power transmission apparatus for a vehicle, theapparatus comprising: a first input shaft fixedly connected to an engineoutput shaft fixedly connected to an engine; a second input shaft formedas a hollow shaft, mounted coaxial with and external to the first inputshaft without rotational interference therebetween, and selectivelyconnectable to the first input shaft; a third input shaft formed as ahollow shaft, mounted coaxial with and external to the second inputshaft, and selectively connectable to the first input shaft; anintermediate shaft and first and second output shafts mounted inparallel with the first, second, and third input shafts; an idle shaftmounted in parallel with the second output shaft; a planetary gear sethaving a first rotation element, a second rotation element, and a thirdrotation element and mounted on an axis of the intermediate shaft, thethird rotation element and one of the first and second rotation elementsbeing selectively connectable to the intermediate shaft, the first andsecond rotation elements being coupled to the third and second inputshafts, respectively; a plurality of gear sets, each of which isconfigured to allow at least one torque flow between the intermediateshaft, the first, second, and third input shafts, the first and secondoutput shafts, the idle shaft, and the planetary gear set; a firstsynchronizer mounted on the first output shaft, selectively receiving afirst torque from the second input shaft through two paths, andtransmitting the received first torque to the first output shaft; asecond synchronizer mounted on the second output shaft, selectivelyreceiving a second torque from the third input shaft through two paths,and transmitting the received second torque to the second output shaft;and four clutches.
 2. The power transmission apparatus of claim 1,wherein the planetary gear set is a single pinion planetary gear set andthe first rotation element, the second rotation element and the thirdrotation element are a sun gear, a planet carrier, and a ring gear,respectively.
 3. The power transmission apparatus of claim 2, whereinthe first and third rotation elements of the planetary gear set areselectively connectable to the intermediate shaft.
 4. The powertransmission apparatus of claim 3, wherein the four clutches include: afirst clutch mounted between the first input shaft and the second inputshaft; a second clutch mounted between the first input shaft and thethird input shaft; a third clutch mounted between the intermediate shaftand the third rotation element of the planetary gear set; and a fourthclutch mounted between the intermediate shaft and the first rotationelement of the planetary gear set.
 5. The power transmission apparatusof claim 2, wherein the second and third rotation elements of theplanetary gear set are selectively connectable to the intermediateshaft.
 6. The power transmission apparatus of claim 5, wherein the fourclutches include: a first clutch mounted between the first input shaftand the second input shaft; a second clutch mounted between the firstinput shaft and the third input shaft; a third clutch mounted betweenthe intermediate shaft and the third rotation element of the planetarygear set; and a fourth clutch mounted between the intermediate shaft andthe second rotation element of the planetary gear set.
 7. The powertransmission apparatus of claim 2, wherein the plurality of gear setsincludes: a first gear set including a first input gear and a firstgear, the first input gear being fixedly connected to the first inputshaft, the first gear being fixedly connected to the intermediate shaftand gear-engaged with the first input gear; a second gear set includinga second input gear and a first shifting gear, the second input gearbeing fixedly connected to the second input shaft, the first shiftinggear being rotatably mounted on the first output shaft and gear-engagedwith the second input gear; a third gear set including a second gear, athird input gear, and a second shifting gear, the second gear beingfixedly connected to the second rotation element of the planetary gearset, the third input gear being fixedly connected to the second inputshaft and gear-engaged with the second gear, and the second shiftinggear being rotatably mounted on the first output shaft and gear-engagedwith the third input gear; a fourth gear set including a third gear anda fourth input gear, the third gear being fixedly connected to the firstrotation element of the planetary gear set, the fourth input gearfixedly connected to the third input shaft and gear-engaged with thethird gear; a fifth gear set including a third shifting gear and asecond idle gear, the third shifting gear being rotatably mounted on thesecond output shaft, the second idle gear being fixedly connected to theidle shaft and gear-engaged with the third shifting gear; a sixth gearset including the fourth input gear and a fourth shifting gear, thefourth input gear fixedly connected to the third input shaft, and thefourth shifting gear being rotatably mounted on the second output shaftand gear-engaged with the fourth input gear; and a seventh gear setincluding the fourth input gear and a first idle gear, the fourth inputgear fixedly connected to the third input shaft, and the first idle gearfixedly connected to the idle shaft and gear-engaged with the fourthinput gear.
 8. The power transmission apparatus of claim 7, wherein theplurality of gear sets further include an eighth gear set including afinal reduction gear of a differential, and first and second outputgears fixedly connected to the first output shaft and the second outputshaft respectively and gear-engaged with the final reduction gear. 9.The power transmission apparatus of claim 7, wherein the first, second,third, and fourth gear sets are mounted in an order of the fourth,third, second and first gear sets from a side of the engine output shafton the first input shaft and the fifth, sixth, and eighth gear sets aremounted in an order of the eighth, sixth and fifth gear sets from theside of the engine output shaft on the second output shaft.
 10. Thepower transmission apparatus of claim 7, wherein the first synchronizeris configured to selectively connect one of the first shifting gear ofthe second gear set and the second shifting gear of the third gear setto the first output shaft; and wherein the second synchronizer isconfigured to selectively connect one of the third shifting gear of thefifth gear set and the fourth shifting gear of the sixth gear set to thesecond output shaft.